Fig. 1.

Comparison of the mouse and human5HT₃R upstream promoter region. Two independent and overlapping mouse genomic clones containing 3 kb and 1.3 kb of genomic DNA, respectively, are shown with respect to the initiator methionine and exon 1 (black boxes) encoding the 5HT₃R. The human 5HT₃R cosmid clone of 20 kb is also depicted with arrowheadsto indicate that the clone continues. Sequence comparison of the proximal 5HT₃R promoter region is shown for the mouse and human sequences with the first nucleotide in the ATG initiator codon assigned as position +1. Conserved elements are boxed and labeled, including the E-Box, Pal-1, and NF1 potential DNA binding recognition sites. The initiator methionine codon of the mouse and human cDNA clones is shown in bold, and the beginning of the mouse5HT₃R cDNA is indicated by anarrow. Large arrowheads show the end positions of the fragment used for the RNase protection assay to determine the major start sites (Fig. 3B). Major start sites are shown with a smaller arrowhead, and thenumber given above each symbol corresponds to the assigned transcriptional start site, as shown in Figure2B.